Image signal compression encoding apparatus and image signal expansion reproducing apparatus

ABSTRACT

A compression encoder uses an arbitrary normalization coefficient and a preset table to achieve a compression of image signal with a desired compression rate. Since the normalization coefficient and the table data are sent to an image signal decoding and reproducing apparatus together with the compressed image data, the reproducing apparatus can restore the original image from those data items. Furthermore, in the encoder, when an amplitude value of the data exceeds a predetermined value, an overflow sensor means the condition so as to produce normalized data in addition to the Huffman-encoded data. The reproducing apparatus achieves the image signal decoding and reproducing operations by use of the normalized data and the Huffman-encoded data. With these apparatuses, the picture quality can be prevented from being lowered due to an overflow in the encoding operation.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image signal compression encodingapparatus and to an image signal expansion reproducing apparatus, and inparticular, to an image signal compression encoding apparatus in whichafter a two-dimensional orthogonal transformation of a video signal, thevideo signal can be normalized by use of a desired normalizationcoefficient and to an image signal expansion reproducing apparatus fordecoding data thus encoded.

2. Description of the related Art

When loading a memory with digital image data such as image data shot byan electronic still camera, in order to reduce the amount of data tominimize the storage capacity of the memory, various kinds ofcompression and encoding operations are performed on the image data.Particularly, two-dimensional orthogonal encoding has been commonlyemployed because the encoding can be accomplished with a highcompression rate and image distortion in the encoding can be suppressed.

In such a two-dimensional orthogonal transformation of a video signal,the image data is subdivided into a predetermined number of blocks. Thetransformation is conducted on image data of each block. Obtained imagedata, namely, a transformation coefficients are compared with apredetermined threshold value and the that portion does not exceed thethreshold value is truncated (i.e. a coefficient truncation isachieved.) As a result, thereafter, any translation coefficients notexceeding the threshold are treated as data of zero in the processing.The transformation coefficients, which have undergone the truncation,are then divided by using a predetermined quantization step value,namely, a normalization coefficient to be quantized or normalizeddepending on the step width. Through the operation above, the value ofthe translation coefficients, namely, the dynamic range of the amplitudecan be suppressed.

The normalized translation coefficients are thereafter encoded. By theway, the transformation coefficients include data items arranged from alow-frequency range to a high-frequency range depending on the magnitudeof each block of the image data. Since the data of the normalizedtransformation coefficients become 0 in the high-frequency component,run-length encoding is achieved in which the original data aretranslated into a continuation length of value 0, namely, a so-calledrun length of 0 and a value of data including values of other than 0,namely, a so-called amplitude of non-zero. The resultant data is thensubjected to a two-dimensional Huffman encoding to produce compressedimage data thus encoded.

In the two-dimensional orthogonal transformation coding, by altering thevalue of the normalization coefficient, the image data can be encodedwith various compression rates. For example, with a large value of thenormalization coefficient, the normalized translation coefficient datatakes a small value. Consequently, the compression rate of the imagedata is increased and the picture quality of the attained data islowered. Conversely, for a small value of the normalization coefficient,the image data is compressed with a small compression rate and hence ahigh picture quality is developed for the attained data.

As a consequence, although the normalization is to be achieved withvarious kinds of normalization coefficients, normalization coefficientdata used in an inverse normalization to be conducted by a reproducingapparatus is required to be changed. This leads to a problem that thenormalization coefficients cannot be arbitrarily selected. Inparticular, after the orthogonal translation, when the compression rateof the encoding is desired to be varied between the low-frequency andhigh-frequency components, there arises a problem of a difficulty insetting the normalization coefficient to the different values.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide an imagesignal compression encoding apparatus wherein normalization of atransformation coefficients after an orthogonal transformation isperformed, and the normalization can be achieved by setting variousnormalization data items which provides an image signal expansionreproducing apparatus capable of appropriately decoding the dataproduced through the compression encoding, thereby solving the problemsof the conventional technology.

In accordance with the present invention, an image signal compressionencoding apparatus in which digital image data constituting a screenimage is subdivided into a plurality of blocks to achieve atwo-dimensional orthogonal transformation encoding on image data of eachblock includes orthogonal transformation means for conducting atwo-dimensional orthogonal transformation of digital image data thussubdivided into plural blocks, normalizing means for normalizing thedata transformed by the orthogonal transformation means, table datastore means for storing therein table data employed by the normalizingmeans for the normalization, encode means for encoding the datanormalized by the normalizing means, and output data generating meansfor generating output data comprising the data encoded by the encodemeans. The output data generating means produces, in addition to thedata encoded by the encode means, the table data used by the normalizingmeans to achieve the normalization.

Furthermore, in accordance with the present invention, an image signalexpansion reproducing apparatus for receiving digital image data of ascreen which has undergone the compression encoding to achieve atwo-dimensional inverse transformation encoding on the data includinginput means for inputting therefrom data comprising image data, decodemeans for decoding image data supplied from the input means, inversenormalizing means for inversely normalizing the data decoded by thedecode means, table data supply means for selecting table data to beemployed by the inverse normalizing means for the inverse normalizationso as to supply the data to the inverse normalizing means, andorthogonal inverse transformation means for achieving a two-dimensionalorthogonal inverse transformation on the data thus inversely normalizedby the inverse normalizing means, the inverse normalizing meansachieving the inverse normalization based on table data included in datasupplied thereto.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and features of the present invention will become moreapparent from the consideration of the following detailed descriptiontaken in conjunction with the accompanying drawings in which:

FIG. 1 is a schematic block diagram illustrating an embodiment of animage signal compression encoding apparatus in accordance with thepresent invention;

FIG. 2 is a block diagram illustrating a non-zero sensor section 18 ofFIG. 1;

FIG. 3 is a schematic block diagram illustrating a zero-run counter 20of FIG. 1;

FIG. 4A is a block diagram illustrating an amplitude sensor section 24of FIG. 1;

FIG. 4B is a schematic diagram illustrating an overflow sensor circuit50 of FIG. 4A;

FIG. 5 is a diagram schematically illustrating an additional-bitcomputing section 26 of FIG. 1;

FIG. 6 is a schematic diagram illustrating a fixed-length itemgenerating buffer 30;

FIG. 7 is a block diagram schematically illustrating an image signalexpansion reproducing apparatus for decoding and for reproducing imagedata compressed and encoded by the compression encoding apparatus ofFIG. 1;

FIG. 8 is a diagram illustrating data obtained through a two-dimensionalorthogonal transformation;

FIG. 9 is a schematic diagram illustrating encoding operationsassociated with the run length and a non-zero amplitude;

FIG. 10 is a diagram illustrating an example of weight table data;

FIG. 11 is a schematic diagram illustrating an example of a normalizedtransformation coefficient;

FIG. 12 is a diagram illustrating relationships between amplitude valuesof the translation coefficient, amplitude ranges thereof, and additionalbits; and

FIG. 13 is a schematic diagram illustrating relationships betweenamplitude values of the transformation coefficient and amplitude rangesthereof.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, a description will be given in detail ofan image signal compression encoding apparatus and an image signalexpansion reproducing apparatus in accordance with the presentinvention.

FIG. 1 illustrates an embodiment of an image signal compression encodingapparatus in accordance with the present invention.

The system includes a blocking section 12, which includes a frame bufferto be loaded with a frame of still video data shot by an electronicstill camera and supplied thereto via an input terminal 10. The imagedata of a frame stored in the blocking section 12 is subdivided into aplurality of blocks. The content of each block is read out therefrom soas to be fed to a two-dimensional orthogonal transformer 14. Thetransformer section 14 achieves a two-dimensional orthogonaltransformation on the image data of each block. The translation may beany one of known two-dimensional orthogonal transformations such as adiscrete cosine transformation and Hadamard transform coding.

The image data of each block which has undergone the two-dimensionalorthogonal translation in the translator 14 is arranged in atwo-dimensional array as illustrated in FIG. 8 such that lower-orderdata is located in the upper-left portion and higher-order data isplaced in the lower-right portion as indicated by arrows. Thetwo-dimensional orthogonal transformer 14 produces an output to be fedto a normalizer 16.

The normalizer 16 conducts a coefficient truncation on the image datawhich has undergone the two-dimensional orthogonal transformation in thetransformer 14, namely, on translation coefficients so as to normalizethe data thereafter. In the coefficient truncation, the transformationcoefficients which have undergone the orthogonal transformation arecompared with a predetermined threshold value to truncate a portion ofdata not exceeding the threshold value. In the normalization, thetranslation coefficients after the coefficient truncation are divided bya predetermined quantization step value, thereby achieving aquantization of the image data.

Connected to the normalizer 16 is a multiplier 34 for inputting thequantization step value to the normalizer 16. The multiplier 34 islinked to a normalization coefficient storage 22 and a selector 36,which is in turn connected to a weight table storage 38. Thenormalization coefficient storage 22 and the selector 36 are connectedto an operator's console 40 for supplying therefrom the system with aninstruction from the operator.

The weight table storage 38 is loaded with data of various kinds ofweight tables Ts, as illustrates in FIG. 10, to be employed for thenormalization in the normalizer 16. The table data items are deliveredto the selector 36. Depending on an instruction of the operator suppliedfrom the operator's console 40, a weight table T is selected by theselector 36 so as to be fed to the multiplier 34. On the other hand,according to an instruction of the operator supplied from the operator'sconsole 40, a normalization coefficient stored in the normalizationcoefficient storage 22 is selectively obtained therefrom so as to besent to the multiplier 34. The weight table content is multiplied by thedata of the normalization coefficient in the multiplier 34, which thusattains a quantization step value to be adopted in the normalization.

The data of the quantization step value in the multiplier 34 aresupplied to the normalizer 16, which divides by the obtained value thetransformation coefficient supplied from the two-dimensional transformer14 has undergone the coefficient truncation, thereby accomplishing thenormalization. The multiplier 34 delivers an output of the quantizationstep value, in addition to the normalizer 16, to a multiplexer 64.

In the translation coefficient, since the low-frequency component ismore effective as data when compared with the high-frequency component,the weight table T as illustrated in FIG. 10 is loaded with, forexample, smaller values in the low-frequency portion and larger valuesin the high-frequency portion. The normalization of the data isaccomplished by dividing transformation coefficients which haveundergone the coefficient truncation by a value αT attained bymultiplying the data of the table T by the normalization coefficient α.Assuming the translation coefficients prior to the normalization to beX, the coefficient X' after the normalization is represented as follows.

    X'=X/(αT)

For example, the table data T is multiplied by α in which thelow-frequency and high-frequency components of the transformationcoefficient X are respectively associated with the low-frequency andhigh-frequency components of the table T. The translation coefficients Xare divided by the resultant value.

As described above, with the provision of the weight table T, in placeof a uniform division of the translation coefficient X by a value α, asmaller value can be adopted as a divider for the division associatedwith the low-frequency portion to minimize the compression rate, whereasa larger value can be used for the division associated with thelow-frequency portion to increase the compression rate. Furthermore,when compressing data in a high picture quality mode, owing to the smallvalue of the normalization coefficient α, by setting a larger value tothe low-frequency component and a smaller value to the high-frequencycomponent of the weight table T, an occurrence of an overflow which willconcentrate on the low-frequency component can be reduced.

The output from normalizer 16 is an n-bit transformation coefficientnormalized as illustrates in FIG. 11. The coefficient represented withn-bit data takes, as can be seen from this figure, a value ranging from2^(n-1) to -2^(n-1). That is, in this example, a half portion includingn-1 bits represents a value of 0 or a value in a range from 2^(n-1) to 1and another half portion including n-1 bits denoting a negative valueranging from -1 to -2^(n-1). Of those values, the negative data itemsfrom -1 to -(2^(n-1) -1) are 2's complements associated with thepositive data items ranging from 1 to 2^(n-1) -1, respectively.

For the normalized transformation coefficient, the n-bit data items arearranged in a two-dimensional array in a similar fashion as employed forthe data items prior to the normalization as illustrated in FIG. 8.These data items are sequentially produced through a zigzag scanning asillustrated in FIG. 9.

The normalizer 16 delivers the output to a non-zero sensor 18, anamplitude sensor 24, and an additional-bit computing section 26.

The non-zero sensor 18 is supplied with transformation coefficient dataincluding n bits as illustrates in FIG. 2 to be received by inverters401, 402, . . . and 40n thereof. These inverters deliver the respectiveoutputs to a NAND circuit 42. Each bit of the n-bit transformationcoefficient data is supplied to the associated one of the inverters 401,402, . . . and 40n as data of "1" or "0". For a data item "1", theinverter produces "0". As a consequence regardless of the outputs fromthe other inverters, the NAND circuit 42 generates an output "1". Thisvalue "1" denotes a non-zero transformation coefficient data, namely,that the n-bit coefficient is other than 0. Conversely, when all bits ofthe translation coefficient data are "0", each inverter produces anoutput "1". Consequently, the NAND circuit generates an output "0". Thisvalue "0" designates a zero transformation coefficient, namely, that then-bit coefficient is 0. The non-zero sensor 18 delivers the output to azero-run counter 20.

The zero-run counter 20 of this embodiment includes an inverter 44 and asix-bit counter 46 as illustrates in FIG. 3. The inverter 44 is suppliedwith the output from the non-zero sensor 18, namely, a zero or non-zerosignal so as to produce an inverted signal thereof. The output from theinverter 44 is inverted so as to be fed to a clear terminal CLR of thecounter 46. On receiving a non-zero signal "1" from the non-zero sensor18, a signal "0" is supplied to the clear terminal CLR to clear thecounter 46. The counter 46 is supplied with a translation coefficienttransfer check clock via a clock input terminal CK from thetwo-dimensional orthogonal transformer 14 so as to count the clocks.When a signal "0" is received by the clear terminal CLR, the count valueis cleared. As a consequence, the counter 46 continues the countingwhile the zero signal "0" being received from the non-zero sensor 18. Inresponse thereto, the length of a zero run is counted in the zigzag scanof FIG. 9.

In this embodiment, the block size is 8×8=64 and the maximum number ofcontinuous zero bits is limited to 64. As a consequence, the zero-runlength can be represented with data including six bits. The zero-runcounter 20 delivers the output to a two-dimensional Huffman encoder 28.

The amplitude sensor 24 is supplied with a translation coefficient fromthe normalizer 16 so as to produce an amplitude range bit and anoverflow signal, which will be described later. As illustrated in FIG.4A, the amplitude sensor 24 includes an absolute value generatingcircuit 48. The absolute value generator circuit 48 receives thenormalized transformation coefficient including n bits from thenormalizer 16 so as to create an absolute value thereof. That is, in acase where the inputted n-bit data is zero or a positive value in arange from 2^(n-1) to 1 of FIG. 11, the received data is directlyoutputted from the circuit 48. Whereas for a negative value in a rangefrom -1 to -2^(n-1), a 2' complement is generated so as to invert thesign symbol and producing an absolute value of the input data.

Of the n bits produced from the absolute value generating circuit 48,n-8 high-order bits are sent to an overflow sensor circuit 50. Thesensor 50 includes, as illustrates in FIG. 4B, an OR circuit 54receiving n-8 inputs. When either one of the n-8 inputs is "1", thecircuit 54 produces an overflow signal "1". In this embodiment, asillustrates in FIG. 12, 8-bit data taking a value ranging from -127 to127 associated with a level of the translation coefficient is compressedand encoded so as to transmit the resultant data. The data beyond therange from -127 to 127 is related to an overflow and hence additionaldata is added to the resultant data for the transmission. As aconsequence, a portion exceeding eight bits, namely, the n-8 high-orderbits include "1", an overflow is assumed and hence the overflow sensor50 produces an overflow signal "1" in this case. The output from thecircuit 50 is supplied to a priority encoder 52 and the additional bitcomputing section 26 of FIG. 1.

The priority encoder 52 is supplied with seven low-order bits of the nbits produced from the absolute value generating circuit 48. Since thetransformation coefficient is data representing an absolute valuecreated by the circuit 48, the data is in a range from -127 to 127 andhence can be represented with seven bits of the original eight bitswhere a bit is removed for use as a sign identification. In thissituation, seven low-order bits of n bits from the circuit 48 areadopted to represent data in the range. As illustrated in FIG. 13, thepriority encoder 52 is responsive to an output OF from the overflowsensor 50 and to the seven low-order bits from the absolute valuegenerating circuit 48 so as to produce three-bit data indicating anamplitude range.

In a case, as illustrated in FIG. 13, where the overflow sensor 50produces a signal "0", the transformation coefficient is expressed withseven low-order bits. Namely, depending on the seven low-order bits, thethree-bit data is generated to indicate the amplitude range. Data of theamplitude range is set as illustrated in FIG. 12 according to the rangeof the data of seven low-order bits included in the translationcoefficient. In FIG. 13, positions denoted by x in the seven low-orderbits may take either one of the values "1" and "0".

For an overflow signal "1", there exists data exceeding eight low-orderbits and hence "000" is produced for the amplitude range, namely, asignal indicating an overflow is generated as shown in FIG. 13.

In this embodiment, a three-bit amplitude range is developed inassociation with a range of the amplitude value as illustrated in FIG.12. For example, for an amplitude value -1 or 1, the amplitude range isdetermined as "001". In a case where the amplitude is in a range from-127 to -64 or from 64 to 127, the amplitude range is attained as "111".Incidentally, the additional bit of FIG. 13 designates the number ofbits necessary for identifying a value of data for which the amplituderange, namely, the range of the amplitude value is specified by thethree-bit amplitude range data.

For example, for the amplitude range data "010" of FIG. 12, availableamplitude values include -3, -2, 2, and 3. In this situation, two bitsare required to specify either one of these four data items.Consequently, three-bit data is necessary to represent data ranging from-3 to 3. However, since the amplitude range data specifies the amplituderange, only two bits are required for the additional-bit data toidentify the data in the range. As described above, when n+1 bits arenecessary to denote the amplitude data itself, if the amplitude range isspecified by the amplitude range data, the additional-bit data needs toonly include n bits.

The amplitude range data produced from the priority encoder 52 is fed tothe two-dimensional Huffman encoder 28 and a fixed-length itemgenerating buffer 30.

The two-dimensional Huffman encoder 28 receives data of a zero-runlength from the zero-run counter 20 and data of an amplitude range fromthe amplitude sensor 24 to achieve a two-dimensional Huffman encodingthereon. In this embodiment, the zero-run length and the amplitude rangeare respectively expressed with six and three bits, namely, nine-bitdata including a combination of these data items is subjected to theHuffman encoding. The two-dimensional Huffman encoder 28 supplied thefixed-length item generating buffer 30 with data of a predeterminednumber of bits (m bits) thus encoded and a length of the encoded data ora so-called Huffman code length.

The additional-bit computing section 26 is includes a subtractor 56 anda selector 58 as illustrated in FIG. 5. This section 26 receives anormalized transformation coefficient from the normalizer 16 and anoverflow signal from the amplitude sensor 24. The subtractor 56 issupplied with data of seven low-order bits of the translationcoefficient and the most-significant bit, MSB, as the highest-order bit.The data of MSB signal is subtracted from the data of seven low-orderbits. The MSB signal is "0" or "1" when the data of the seven low-orderbits is positive or negative, respectively. The subtractor 56 sends asubtraction result represented with data including at most seven bits toan input A of the selector 58.

The selector 58 has another input B, which directly receives the n-bittransformation coefficient from the normalizer 16. Furthermore, theselector 58 receives an overflow signal from the amplitude sensor 24.For an overflow signal "0" indicating the absence of an overflow, theselector 58 selects data including at most seven bits received from theinput A. For an overflow signal "1" denoting the presence of anoverflow, the selector 58 selects the n-bit translation coefficient dataattained from the input B. As a consequence, the data outputted from theadditional-bit computing section 26 includes at most seven bits or then-bit data depending on the absence or presence of an overflow,respectively.

The fixed-length item generating buffer 30 includes, as illustrated inFIG. 6, a bit length computing section 60 and a buffer 62. The bitlength computing section 60 is supplied with the amplitude range datafrom the amplitude sensor 24 and the Huffman code length from thetwo-dimensional encoder 28. Based on the amplitude range and the Huffmancode length, the computing section 60 determines the total number ofbits included in data obtained through the Huffman encoding andadditional-bit data to be added thereto so as to supply the buffer 62with an address signal for a write operation of the data associated withthe number of bits. Since the additional-bit data includes at most sevenbits when an overflow does not occur and n bits at an occurrence of theoverflow, a signal including the additional-bit data and the bits ofdata obtained through the Huffman encoding is delivered to the buffer62.

The buffer 62 further receives additional bits ranging from one bit to nbits from the additional-bit computing section 26 and theHuffman-encoded data from the two-dimensional Huffman encoder 28.Depending on the total data length of the encoded data and theadditional-bit data, the bit length computing section 60 produces anaddress signal. These data items are written in the buffer 62 at anaddress designated by the address signal.

The data stored in the buffer 62 is transmitted to the multiplexer 64 ofFIG. 1 after the Huffman-encoded data is combined with theadditional-bit data so as to be sent thereto in the unit of dataincluding a predetermined number of bits. The multiplexer sequentiallyselects the encoded data sent from the fixed-length item generatingbuffer 30 or the quantization step value supplied from the multiplier34. The selected data or value is sent from an output terminal 32 to atransmission route or is written on a recording medium such as amagnetic disk.

According to a compression encoder as described above, the input imagedata is subdivided into a plurality of blocks by the blocking section 12for undergoing the two-dimensional orthogonal translation by thetwo-dimensional orthogonal transformer 14. The transformationcoefficient attained through the orthogonal translation is subjected tothe coefficient truncation and the normalization as described above. Theresultant data is sent to the non-zero sensor 18 and the amplitudesensor 24 sense the non-zero and the amplitude, respectively.Thereafter, the zero-run length attained by the zero-run counter 20 andthe amplitude range data from the amplitude sensor 24 are subjected tothe two-dimensional Huffman encoding in the two-dimensional Huffmanencoder 28.

The encoded data is checked in the fixed-length item generating buffer30 to determine whether or not an overflow occurs in consideration ofthe amplitude range data. If an overflow does not occur, the additionalbit data ranging from one bit to seven bits is produced for the encodeddata. Otherwise, the additional bit data including n bits is added tothe encoded data.

Consequently, when the overflow does not occur, the which data hasundergone the two-dimensional Huffman encoding and the additional-bitdata including the fewer number of bits is transmitted or recorded so asto achieve the compression encoding of image data. On the other hand, atan occurrence of an overflow, the produced data includes the encodeddata and the additional-bit data. As a consequence, the additional bitrepresents the image data itself. As a result, in a reproduction of theimage data, the picture quality is prevented from being deteriorated dueto the overflow.

In the conventional compression encoder, when the amplitude of thenormalized translation coefficient is beyond the predetermined range,namely, when the number of bits of the transformation coefficientexceeds the number of the present bits, a data overflow takes place. Forexample, in the n-bit data as illustrated in FIG. 11, if the amplituderange is specified as n-1 bits, when the n-bit data takes a negativevalue, the data "1" of the upper-most bit is ignored so as to set theamplitude range based on the other n-1 bits. Since the produced dataincludes the additional bit which data has and the data undergone theHuffman encoding based on the amplitude range and the zero-run length,when decoding the data, it is impossible to decode the data "1" of theupper-most bit. Namely, the same decoding result is attained from thedata items respectively having "1" and "0" at the upper-most position.As a result, an image displayed with the decoded image data is attendedwith an inversion in white and black portions and hence the picturequality is deteriorated.

Particularly, in order to reduce the compression rate, when the value ofthe normalization coefficient employed by the normalizer 16 for thenormalization is reduced, the normalized transformation coefficientstakes a large value. As a consequence, an overflow is likely to occurand hence the picture quality is lowered. Namely, this leads to adisadvantage that even if the compression rate is minimized to attain ahigh picture quality, it is impossible to develop the desired picturequality.

In contrast thereto, according to the apparatus of the embodiment, whenan overflow occurs based on the preset amplitude range, the systemproduces output data by adding the additional-bit data representing theimage data to the encoded data which has undergone the compressioncoding. As a consequence, the value of the image data is denoted by theadditional-bit data. By decoding the additional-bit data, the originalimage data can be reproduced and hence no deterioration of the picturequality due to the overflow occurs.

Furthermore, the amplitude range data specifies the amplitude range,namely, a range of the amplitude value. The range data isHuffman-encoded together with the zero-run length. Consequently, whendata causes an overflow as described above, since the data represents avalue obtained by removing the value in the range specified by theamplitude range data, the value of additional bits to identify the datacan be expressed with bits of which the number is less by one than thenumber required to represent the data itself.

For example, as illustrated in FIG. 12, when the amplitude value data isin a range from -255 to -128 and in a range from 128 to 255, theamplitude value data can be identified by additional-bit data includingeight bits. In a case where the amplitude value data is in a range from-255 to 255, although nine-bit data is naturally necessary to expressthis data, since the data in the range from -127 to 127 is beforehandremoved, the data can be identified by eight bits.

In addition, with the provision of the weight table T, in place of theoperation to uniformly divide the translation coefficient by a value α,various values can be used for the normalization depending on thecomponents of the translation coefficient. For example, for thedivision, smaller and larger values may be employed for thelow-frequency and high-frequency components, respectively. In this case,for the compression encoding operation, a smaller compression rate canbe applied to the low-frequency components which are more effective asdata, whereas a larger compression rate can be used for thehigh-frequency components which are less effective as data. As a result,the compression rate as well as the picture quality can be increased.Conversely, when a large compression rate is adopted for thelow-frequency component in the compression encoding, the overflow can beprevented.

The weight table T may be loaded with arbitrary predetermined data.Moreover, data inputted from the operator's console 40 to specify aweight table T and data supplied from the console 40 to specify anormalization coefficient or the table data itself may be delivered tothe multiplexer 64 such that an encoding is achieved by use of thesedata items in a decoder, which will be described later.

FIG. 7 illustrates an embodiment of an image signal expansionreproducing apparatus in accordance with the present invention. Thisapparatus is employed to achieve an expansion playback operation ofimage data encoded by the encoder of FIG. 1.

The configuration of FIG. 7 includes a Huffman decoder 72, which has aninput terminal 70 to receive image data generated through thecompression encoding in the compression encoder of FIG. 1. Namely, theinput terminal 70 receives data obtained through the Huffman encodingachieved by the two-dimensional Huffman encoder 28 of the systemillustrated in FIG. 1 and the additional-bit data generated by theadditional-bit computing section 26 of the system. Of these data items,the Huffman-encoded data is fed to the Huffman decoder 72. The Huffmandecoder 72 decodes the received data based on data transmitted from aHuffman table, not shown, so as to obtain data of the zero-run lengthand data of the non-zero amplitude range. The zero-run data and thenon-zero amplitude range data created from the Huffman decoder 72 aredelivered to a zero-run generator 74 and a transformation coefficientdecoder 76, respectively. Moreover, the Huffman decoder 72 outputs azero/non-zero switch signal to a multiplexer 78.

On the other hand, the additional-bit data from the input terminal 70 issupplied to the transformation coefficient decoder 76.

The zero-run generator 74 produces, based on the zero-run length datafrom the Huffman decoder 72, data of zeros of which the number isassociated with the run length. That is, the number of zeros isequivalent to the run length. The zero-run data created from thezero-run generator 74 is transmitted to the multiplexer 78.

The transformation coefficient decoder 76 decodes an n-bit non-zerotranslation coefficient based on the non-zero amplitude range data fromthe Huffman decoder 72 and the additional-bit data from the inputterminal 70. If the amplitude range data is other than "000", it isindicated that the overflow sensor 50 of the apparatus of FIG. 1 has notsensed an overflow. Consequently, the translation coefficient decoder 76accomplishes the decoding by use of the three-bit amplitude range dataand the additional-bit data to compute the non-zero translationcoefficient. If the amplitude range data is "000", the overflow sensor50 of the apparatus of FIG. 1 is assumed to have sensed an overflow.Consequently, the transformation coefficient decoder 76 achieves thedecoding by use of the additional-bit data to attain the non-zerotransformation coefficient. In a case of an occurrence of an overflow,since the non-zero transformation coefficient itself has beentransmitted as the additional-bit data, this data is directly adopted asan output from the decoded transformation coefficient. Thetransformation coefficient decoder 76 delivers the output to themultiplexer 78.

The multiplexer 78 selects, depending on the zero/non-zero switch signalfrom the Huffman decoder 72, the zero-run data from the zero-rungenerator 74 or the n-bit non-zero transformation coefficient from thetransformation coefficient decoder 76. When the zero/non-zero switchsignal indicates zero, the zero-run data from the zero-run generator 74is selected. Whereas, when the non-zero is indicated, the n-bit non-zerotransformation coefficient from the transformation coefficient decoder76 is used. The multiplexer 78 delivers the output to an inversenormalizer 80.

The inverse normalizer 80 is supplied with, in additional to image datafrom the input terminal 70, data of a product αT between thenormalization coefficient and table data. Based on the data αT. theinverse normalizer 80 inversely normalizes the decoded data from themultiplexer 78. That is, the data αT is multiplied by the decoded imagedata from the multiplexer 78 so as to achieve the inverse normalization.The decoded image data from the multiplexer 78 includes encoded dataobtained through a normalization by use of the weight table T asillustrated in FIG. 10. As a consequence, data as a result of amultiplication between the normalization coefficient α and the weighttable data T is supplied to the input terminal to conduct the inversenormalization. By multiplying the data from the multiplexer 78 by thedata αT, the inverse normalization is accomplished.

The inverse normalizer 80 sends the output to a two-dimensional inversetransformer 82, which conducts a two-dimensional orthogonal inversetransformation on the inversely normalized data from the inversenormalizer 80. The two-dimensional inverse transformer 82 transmits theoutput to a block composer 84, which combines a plurality of blocks intoimage data of an overall screen. The block composer 84 delivers theoutput to a cathode-ray tube, CRT 86 to reproduce the image thereon. Bythe way, in lace of the CRT 86, there may be disposed, for example, aprinter to which the output is supplied so as to produce a print.

In accordance with the image signal reproducing apparatus above, theimage data which has undergone the compression encoding in the encoderof FIG. 1 can be reproduced through the expansion.

In accordance with this apparatus, since the inverse normalizer 80achieves the inverse normalization based on the image data from theinput terminal 70 and the data of the product between the normalizationcoefficient α and the weight table T, the decoding can be carried out inassociation with the normalization coefficient and the weight tableemployed in the encoding. As a consequence, encoded data items obtainedthrough various encoding operations depending on image data items can beappropriately decoded, for thereby reproducing the image data.

As described above, when data encoded by use of a weight table is to bedecoded, it is possible in the decoding operation, for example, to adopta small value and a large value as the divider in the normalization ofthe low-frequency and high-frequency components, respectively. As aconsequence, since the decoding is achieved on encoded data through anencoding such that a smaller compression rate is applied to thelow-frequency component which is more significant as data and that alarger compression rate is used for the high frequency component whichis less effective as data, the reproduced image develops a high picturequality. Furthermore, the low-frequency component is encoded with alarge compression rate so as to prevent an occurrence of the overflow.The obtained data is decoded to reproduce an image with a high picturequality.

According to the image signal reproducing apparatus above, since thedecoding can be achieved depending on the received weight table data,and also in a case where various weight tables are used in the imagedata encoding, the respective image data can be appropriately decoded.

Furthermore, in this reproducing apparatus, as described above, theencoded data from the input terminal 70 is decoded by the Huffmandecoder 72 to obtain the zero-run length and the non-zero amplituderange. Thereafter, the zero-run generator 74 and the transformationcoefficient decoder 76 produce data of zeros of which the number isassociated with the run length and the non-zero translation coefficientdata. When the amplitude range is within a predetermined range, thetransformation coefficient decoder 76 decodes the transformationcoefficient by use of the amplitude range data and the additional-bitdata. When the amplitude range is beyond the predetermined range, thetransformation coefficient is produced by use of the additional-bit dataincluding n bits. As a consequence, also in a case where the amplituderange is beyond the predetermined range, the translation coefficient canbe generated from the additional-bit data. With this provision, it ispossible to prevent the occurrence of missing data taking place due to adata overflow in the conventional system in which the decoding isconducted only by use of the amplitude range data. As a result, thepicture quality deterioration caused by the data overflow does notappear.

As above, in accordance with the reproducing apparatus, data of thezero-run length and data of the non-zero amplitude range, which eachundergone the Huffman encoding, and the additional bit data at anoccurrence of an overflow are decoded so as to reproduce an image. As aconsequence, image data which has undergone the compression encodingbased on an amplitude range can be decoded for the playback of the data.Moreover, also when an overflow occurs with respect to the amplituderange in the compression encoding, the image can be reproduced by use ofthe additional-bit data.

In accordance with the present invention, since the compression encoderemploys table data in the normalization after the orthogonaltransformation, various kinds of normalization can be achieved bysetting associated table data. Consequently, the compression rate can bearbitrarily set. Furthermore, the overflow in the encoding of image datacan be prevented.

In addition, since the table data adopted in the normalization is sentfrom the compression encoder to the reproducing apparatus, the tabledata can be used for the inverse normalization in the reproducingapparatus so as to decode image data depending on the data employed inthe encoding operation.

While the present invention has been described with reference to theparticular illustrative embodiment, it is not to be restricted by thoseembodiments but only by the appended claims. It is to be appreciatedthat those skilled in the art can change or modify the embodimentwithout departing from the scope and spirit of the present invention.

What is claimed is:
 1. An image signal compression encoding apparatus inwhich digital image data for a screen is subdivided into a plurality ofblocks so as to achieve a two-dimensional orthogonal transformationencoding on image data of each block comprising;orthogonal transformingmeans for conducting a two-dimensional orthogonal transformation of thedigital image data thus subdivided into the plurality of blocks;normalizing means for normalizing the data transformed by saidorthogonal means; table data store means for storing therein table dataemployed by said normalizing means for the normalization; encoder meansfor encoding the data normalized by said normalizing means; and outputdata generating means for generating output data including the dataencoded by said encoder means, said output data generating meansproducing, in addition to the data encoded by said encoder means, thetable data used by said normalizing means to achieve the normalization.2. An apparatus in accordance with claim 1, wherein said normalizingmeans uses, in addition to the table data, a normalization coefficientso as to divide the data which has undergone the orthogonaltransformation by data obtained from multiplying the normalizationcoefficient by the table data, thereby achieving the normalization. 3.An apparatus in accordance with claim 1 further comprising;overflowsense means for sensing a condition that an amplitude value of thenormalized data is beyond a predetermined range, said output datagenerating means producing in the condition where the amplitude value ofthe normalized data is beyond the predetermined range and the conditionis sensed by said overflow sense means, data identifying the normalizeddata in addition to data encoded by said encoder means.
 4. An apparatusin accordance with claim 3, wherein;when said overflow sense means failsto sense the condition that the amplitude value of the normalized datais beyond the predetermined range, said output data generating meansproduces, in addition to the data encoded by said encoder means,additional-bit data including at most seven bits; and when said overflowsense means senses the condition that the amplitude value of thenormalized data is beyond the predetermined range, said output datagenerating means produces, in addition to the data encoded by saidencoder means, data identifying the normalized data, said identifyingdata including bits of which a number less than a number of bits of thenormalized data by one.
 5. An apparatus in accordance with claim 3,wherein;said overflow sense means includes an absolute value generatingcircuit for computing an absolute value of transformation coefficientssupplied thereto and an OR circuit for receiving a predetermined numberof high-order bits from said absolute value generating circuit such thatthe condition that the amplitude value of the normalized data beingbeyond the predetermined range is sensed by use of an output producedfrom said OR circuit.
 6. An image signal exapnsion reproducing apparatusin which digital image data of a screen which has undergone thecompression encoding is received so as to achieve a two-dimensionalinverse transformation decoding on the received data comprising;inputmeans for inputting therefrom data including image data; decode meansfor decoding image data supplied from said input means; inversenormalizing means for inversely normalizing the data decoded by saiddecode means; table data supply means for selecting table data to beemployed by said inverse normalizing means for the inverse normalizationso as to supply the data to said inverse normalizing means; andorthogonal inverse transformation means for achieving a two-dimensionalorthogonal inverse transformation on the data thus inversely normalizedby said inverse normalizing means, said inverse normalizing meansachieving the inverse normalization based on table data included in datasupplied thereto.
 7. An apparatus in accordance with claim 6, whereinsaid inverse normalizing means uses, in addition to the table data, aninverse normalization coefficient for multiplying the data decoded bysaid decode means by data obtained by multiplying the inversenormalization coefficient by the table data, for thereby achieving theinverse normalization.
 8. An apparatus in accordance with claim 6further comprising;data select means for selecting at least one of theimage data decoded by said decode means and the image data supplied fromsaid input means; and overflow sense means for sensing a condition thatan amplitude value of the input data is beyond a predetermined rangebased on the data decoded by said decode means, said data select meansselecting, when said overflow sense means senses the condition that theamplitude value of the input data is beyond the predetermined range, theinput image data in addition to the image data decoded by said decodemeans.
 9. A method for achieving a two-dimensional orthogonaltransformation encoding on digital image data for a screen subdividedinto a plurality of blocks, comprising the steps of:(a) conducting atwo-dimensional orthogonal transformation of the digital image data thussubdivided into the plurality of blocks; (b) normalizing the datatransformed at said step (a); (c) storing table data employed at saidstep (b); (d) encoding the data normalized at said step (b); and (e)generating output data including the data encoded at said step (d) andthe table data used at said step (b).
 10. A method in accordance withclaim 9, wherein said step (b) divides the data transformed at said step(a) by multiplying a normalization coefficient with the table data forachieving the normalization.
 11. A method in accordance with claim 9,further comprising the step of:(f) sensing a condition that an amplitudevalue of the normalized data is beyond a predetermined range andgenerating data identifying the normalized data at said step (e) whenthe amplitude value of the normalized data is beyond the predeterminedrange.
 12. A method in accordance with claim 11, wherein additional bitdata including at most seven bits are produced at said step (e) whensaid step (f) fails to sense that the condition of the normalized datais beyond the predetermined range and data identifying the normalizeddata when said step (f) senses the condition of the amplitude value ofthe normalized data being beyond the predetermined range, saididentifying data including bits of a number less than a number of bitsof the normalized data by one.
 13. A method in accordance with claim 11,wherein said step (f) computes an absolute value of transformationcoefficients supplied thereto and receives a predetermined number ofhigh-order bits such that the condition that the amplitude value of thenormalized data being beyond the predetermined range is sensed.